Signal tuned radio apparatus



' o. GIERWIATOWSKI SIGNAL TUNED RADIO APPARATUS Dec, 16, 1952 3 Sheets-Sheet l Filed Dec. l5, 1950 Dec. 16, 1952 o. Gn-:RwlATowsKl SIGNAL TUNED RADIO APPARATUS 5 Sheets-Sheet 2 Filed Deo. l5, 1950 C A TIIODE l l/Vf' C4 771/005 l l/Vf Dec. 1'6, 1952 O. GIERWITOWSKI y SIGNAL TUNED RADIO APPARATUS 5 Sheets-Sheet 5 Filed Dec. 15, 1950 @www 12@ Mja@ Q/f Patented Dec. 16, 1952 UNITED STATES PATENT OFFICE SIGNAL TUNED RADIOAPPA-RATU S Olgierd Gerwiatowski, Oak'Park, Ill., assigmor,v

/bymesne assignments, to General Motors Gorporation, Detroit, Mich., acorporationof Dela- Ware `ApplicationDecember 15, 1950, Serial N0. 200,911

(Cl. Z50-10) lClaims. l This invention relates to signal tuned radio apparatus. Signal Vtunedradio receivers `require no manual presetting-to tune in progressively` all transmitted signals of sufficient strengtlrwithin the` frequency tuning rangeof the receiver. `Signal tuned radio apparatus hasbroa'd utility and is applicable to home receivers and other' radio apparatus as; well l as automobile receivers and otherreceivers Which are subject to frequent changes of geographical position.

- Signal tunedY receivers have also been knovvnin theart as stop-on-signal, stop-on-carrier, or signal seeking receivers. Signal tuned apparatus of this U general type has been described and claimed in otherpatents, sucli'asv those of E. F; Andrews Patent No 2,493,741and-l O. Gierwiatowski Patent No. 2,494,235, and in U.V S.' Patent No. 2,541,018, granted February 13, 19'51, to E: F. Andrews. yThe present invention is applicable generally v-to resonant responsive` electronic apparatus, but relates especiallyto improvements insignal tuned radio devices.

An'object of this invention is to provide improved` signal tuned devices.

Another Objectis to provide improved signal tuned radio -receivers.

A further objectris to provide an improved radio apparatus in Whicha utilization device is operated when a variable-frequency signal=comes within a narrow frequency band.

Another object is-to provide signal'tuned radioA VAnother Objectis to provide signal tuned radio.

receivers'having improved ability to produce llarge restraining voltages and thereby to utilize relatively 'large actuating. voltages.

Another object is to provide an improvedY signal tuned radio receiver` having improved, restraining voltage producingI means includingA a triode restraining voltage rectifier havinghigh input impedance.

Another object` `is to` provide va signaltuned radio receiver having improved restraining voltage producing means including a tuned primary, a secondary having a large number. ofturns and inductively coupled very closely to .the primary, and a triode rectifier supplied by the secondary.

Another object is to provide a signal tuned radio receiver havingv improved operating volt"- age producing means including a tuned'primary, a secondary coupled veryV closely to the,A primary, aninnite impedance restraining' voltage rectier supplied by the secondary, a tuned secondary coupled'ito the primary, an actuating voltage' rectier supplied by the tuned secondary', meansinterconnecting the recti'ers' in" opposition, `and means providing` a delay bias on the restraining voltage rectifier.

Another object is to provide an improvedijsignal tuned radio receiver in which equal, oppositelyv polarized restraining `and actuatingv voltages are derived from primary and-secondary windings of a single transformer.

Anotherobject is to provide anr improved signal tuned radio receiver in which equal;oppo sitely polarized restrainingvandactuating voltages are derived from two secondaries of asingle transformer.

Another Objectis toprovide animproved-signal tuned radio: receiver` in4 which equal, .oppositely polarized restraining andactuating lvoltages are derived respectively romanvuntuned secondary and a tuned secondary of ai.sing'le transformer having a tuned primary.

Another Objectis toprovide an improved. signal tuned radio receiver having a tuneroperating system responsive to voltages of-bothpolaritieS, and in which arestrainngvoltage biases an actua-ting,` voltage. rectier. so that only sig,- nals having thepolarity of the actuatingvoltage are impressed upon the tuner operating system.

Another object is to provide an improved. signal tuned radio: receiver in which signals for operating the tuner. mechanism areampliiledjgby the audio system of the receiver, and inwhich. a

restraining voltage biases an actuating voltage,

tively polarzed signals -for utilizing the operating signals.

Another object is to provide an improved signal tuned radio receiver having a restraining voltage rectifier and an actuating voltage rectifier, at least one of which is a crystal rectifier, and means to connect the outputs of the rectifiers in series opposition.

Another object is to provide an improved signal tuned radio receiver in which restraining and actuating voltage rectifiers have respective output resistors connected in series opposition, and in which tuner operating means, responsive effectively only to signals having the polarity of the actuating voltage, is coupled to the series connected resistors by a capacitor and a resistor having sufficiently large valves to prevent spurious reversals.

Another object is to provide a signal tuned receiver having in a large measure the qualities desired in such a receiver by utilizing to the fullest extent the apparatus present in an ordinary radio receiver with the addition of the minimum amount of further apparatus to effect signal tuning of the receiver.

Another object is to provide a signal tuned receiver by the addition to the ordinary receiver of simple tuner moving and stopping means, utilizing the audio amplifier for operating these means, and adding a single rectifier to increase the selectivity and the uniformity of the tuning signal.

Another object is to provide a signal tuned receiver in which the effective tuning voltage is confined to a narrow band of frequencies close to the tuning frequency and in which the width of this band does not increase substantially with the strength of the signal which is being signal tuned.

Another object is to provide a signal tuned receiver, possessing the above qualities, which is low in cost and in which the minimum addition of apparatus is made for effecting signal tuning.

Another object is to provide signal tuned apparatus in which selectivity and tuning uniformity are obtained Without undue signal attenuation.

Another object is to provide an economical signal tuned apparatus having sensitive stopping means which will respond to a relatively low voltage tuning signal.

Still another object is to provide a signal tuned radio receiver in which the same tuned circuit and the same rectifier provide the actuating voltage during tuning and the detector voltage during listening.

Further objects, advantages and features of this invention will be apparent from the following description of several illustrative embodiments taken with the drawings in which:

Fig. 1 is a diagrammatic representation of an illustrative signal tuned radio receiver constructed in accordance with the invention;

Fig. 2 is a sectional view on an enlarged scale illustrating the mounting of a spring which drives the tuner of the receiver;

Fig. 3 is a sectional view of a transformer which couples the last intermediate frequency amplifier to the tube which functions as a detector for listening and as an actuating voltage rectifier for tuning;

Fig. 4 is a vfragmentary elevational View illustrating a modification of the transformer of Fig. 3;

Fig. 5 is a perspective view illustrating the eX- ternal appearance of the receiver;

Fig. 6 is a fragmentary diagrammatic View of a modified signal tuned receiver;

Fig. 7 is a fragmentary diagrammatic View of another modified receiver; and

Fig. 8 is a diagrammatic View of still another modified receiver.

Certain features of the receivers disclosed in this application, relating for example to the tuning mechanism, are disclosed and claimed in the copending application of Edward F. Andrews, Serial No. 195,161, filed November 13, 1950. Other features disclosed herein will be claimed in other copending applications.

The signal tuned radio receiver illustrated in Fig. 1 has many of the components of the usual superheterodyne receiver. It has a radio frequency amplifier I8 with an input to which an antenna I2 may be connected. A superheterodyne converter stage I4 is coupled to the output of the R. F. amplifier Il). The converter I4 may include a first dectector, an oscillator, and an I. F. input transformer for coupling the output of the rst detector to an intermediate frequency ampliiier tube I6.

The output of the I. F. tube I6 is coupled to a diode-triode tube I8 which functions as the detector for listening and as the operating voltage rectifier for signal tuning. The output of the detector tube I8 is coupled to a first audio amplifier comprising a triode section of a second diodetriode tube 2li, the diode section providing automatic volume control voltage. The output of the triode section of the tube 20 is coupled by a capacitor 2I to a second audio amplifier tube 22 having an output transformer 24 in its plate circuit. The tubes 28 and 22 function as amplifiers during both listening and signal tuning. A speaker 26 is provided for listening.

The receiver includes a radio frequency tuning inductance 2B, a first detector tuning inductance 3U, and an oscillator tuning inductance 32 which are connected with the corresponding portions of the circuit by means of pairs of leads X, Y and Z, respectively. For convenience and clarity only the end portions of the leads are shown. The inductance coils 28, 38 and 32 are mounted with their axes parallel. The coils are tunable by means of cores or slugs 34, 36 and 38 which are movable in an axial direction.

The cores may be moved by any suitable moving means, such as a motor or a spring which is charged periodically, either manually or by power operated means, such as a solenoid. A variable condenser or other tuning means may be employed in place of the tuning coils and cores. A suitable tuning arrangement including a manually chargeable spring is shown in Figure 1.

The tuning cores 34, 38 and 38 are mounted on a crosspiece 4I) which is supported by a rack member 42. The rack 42 is sldably mounted on a supporting rod 44. The crosspiece is sldably guided by a pushrod or control plunger 48 to restrain the rack from rotation on the supporting rod 44 and to maintain alignment between the cores 34, 36 and 38 and the coils 28, 38 and 32. A knob 48 is provided on thefront end of the pushrod 45 for manually pushing the rod inwardly, and a helical return spring 58 is positioned around the pushrod to urge it outwardly. A C-washer or abutment 52, mounted on the pushrod 46, is engageable with the front of the crosspiece 40 when the pushrod is pushed in- Wardly.

If desired, the crosspiece 48 may be folded downwardly to bring the coils 28, y3l) and 32 underneath ,the rack 42. `Such a modicaton provides'a more. compact tuning mechanism. However. for clarity the coils and the rack are shown on the same level in Fig. l.

The rackl 42 meshes with a pinion 54. A torsional coil spring 58 produces a clockwise torque on the pinion so as to urge the rack outwardly.

As best shown in Fig. 2, the pinion 54 is rotatably carried on a stationary upright shaft 51. The lower end of the torsional coil spring 51B is hooked on ya radial pin 59 fixed to the pinion 54. Thespring 56 is coiled around the outer periphery of a sleeve 8| which may be formed integrally with the pinion and extending upwardly therefrom. The upper end of the coil spring may be.v hooked on a setscrew 63 which is threaded into a collar 85, positioned above the sleeve 6|, or the spring may be attached directly to the collar by other appropriate means. The collar 65 may be attached to the shaft 51 by tightening the setscrew E3. The spring 56 may be given ran initial torsional strain by loosening the setscreW 63, twisting the collar' 85v and tightening the setscrew again.

A pawl 58 is pivoted on a gear wheel 60 rotatably carried on the shaft 51 below the pinion 54. A tension coil spring stretched between the pawl 58 and the gear 60 urges the pawl into engagement with the pinion 54. `The gear 60 meshes with a pinion '62 xed to a second gear wheel 64 which meshes with a pinion E6. A wind vane 69, in the form of a paddle wheel, preferably having two or more Iarms, is mounted on the stopping ymember |68.

A relay 1|) has an armature 12 which is urged toward the brake disc B3 by means of a spring 14. The tension exerted by the spring 14 may be adjusted by means of a screw 16.

The relay 18 has a pair of oppositely polariz- -able windings 18 and 80, the winding 18 operating to attract the armature 12 Iand the winding 80 operating to release the armature. The relay has a core 82 mounted in a frame 84. The magnetic circuit formed by the core 82, the frame 84 and the armature 12 has considerable retentivity so that the armature may be retained in attracted position by residual magnetism, once it has been moved to attracted or closed position by energization of the winding 18. Energization of the Winding 88 releases the armature by bucking the residual magnetism.

The receiver is powered by a battery 88 which may be an automobile battery. A switch 85 is in Aseries with the battery lead. The battery is utilized to energize the winding 18 for attracting the armature 12 to commence tuning. The attracting winding' 18 of the relay 10 is connected across the battery 86 through a starting switch 81 comprising -a pair of contact springs 88 and 90. The contacts 88 and 86 are normally held open by engagement of the washer 52 on the pushrod 48 with a spring member 92 mechanically connected with the contact spring 88 but electrically insulated therefrom. When the knob 48 onr the pushrod is pushed inwardly, the washer 52 is disengaged from the spring member 92 and the spring member closes the contacts 88 and 93. The contacts are shunted by a bleeder resistor 94 which permits a small current to ilow through the attracting winding 18 when the contacts are open to augment the residual magnetism and to provide an Iadjustment of the force tending to hold the armature in attracted or closedA position. If the bleeder current or the retentivity 'of'y themagnetic material is` suitably.A

increased; the relay. armaturemay be. movedgto closed position by a directly applied manual movement if desired. Under these circumstancesl the closing winding and the starting switch would be eliminated.

The relay operates switch means SSincluding anumber of movable contacts.. A movable contact |65 is movable between stationary contacts |02 land les for connecting a secondary winding |05 of the output transformer 44'with, the speaker 26 when the armature 12 is released and with the releasing winding 89 when thearmature 1'2 is attracted. Thus the output transformer is connected with the speaker for listening and with the releasing winding for tuning.

Plate voltage for the receiver is supplied by: a vibrator B supply |86 having two B-loutput conductors |88 and H0. rlhe B supply Iis connected with the battery 86 through a switch and an interference filter comprising a series inductance H4 and a pair of shunt capacitors It and i8.

An I. F. output transformer |28--fcouples the intermediate frequency amplifier pentode I6 with the detector tube |8. The transformer |28 has a primary winding |22 connectedbetween the anode of the pentode l5 and the B supply conductor |88. The primary |22 is shunted by a capacitor |25, to form a tuned circuit.

A secondary tuned circuit comprisingv ya secondary winding |28 in parallel with aI capacitor |28 is coupled with the primary winding |22. One end of the tuned secondary winding |25 .is connected to the anode |39 of the diode section of the tube V 8. The diode section may be termed the actuating voltage rectifier and the Winding |25, the actuating voltage winding. The other end of the secondary winding |28 is connected with the cathode of the diode-triode tube I8 through a series circuit including an intermediate frequency filtering resistor |32, a volume control and diode load resistor |362, and a cathode load resistor |35. Two intermediate frequency bypass capacitors |31 are connected respectively between the ends of the filtering resistor |32 and ground.

The I. F. output transformer |28 has an untuned secondary winding |38 which is closely coupled to the primary winding |22. The winding |38 may be termed the restraining voltage winding. The windings |22 and |38 may constitute a single winding of multiple strand Litz Wire, some of the strands being used for the primary winding |22 and others being used for secondary winding |38. A ferromagnetic core |43 axially movable within the winding |22 may rbe provided to tune the primary circuit, comprising the winding |22 and capacitor |24, to resonance. The secondary windingV |28 may be carried in axially spaced relation to the winding |22 and |38. A second ferromagnetic core |45 may be provided to tune the secondary circuit, comprising winding |26 and capacitor |28, to resonance. The coupling between the primary winding |22 and the secondary winding |28 may be changed, Ifor instance, by adjusting the axialY spacing of the two windings.

Fig. 3 illustrates details of the I. F. .transformer |20. Asindicatedabove,thetunedprimarywinding |22 .and the untuned seconda-ry winding |38 may be wound as a single vcoil |25 of multiple strand Litz wire in order to obtain the closestpossible coupling. As shown in Fig. 3, the Litz wire may have five independently insulated strands.

Three of the strands may be used for the, primaryl escasos winding |22, and the other two strands for the untuned secondary |38. The individual strands must be adequately insulated to isolate the plate voltage.

The coil |25 maybe wound on a short insulating tube |21 which i-s slidably carried on the outside of a longer insulating tube |29. The tuned secondary winding |26 may be wound on the insulating tube |29 -below the coil |25. lThe cores |43 and |45 are threaded into the opposite ends` of the tube |29. The coupling between the coils |25 and |26 may be adjusted by sliding the short tube |21 along the tube |29 to move the coil |25. The positions of the cores |43 and |45 may be adjusted by screwing the cores in or out.

Fig. 4 illustrates a modification of the transformer of Fig. 3. I-f desired, the primary |22 and the secondary |38 may be formed as shown from two separate wires, wound side by side or twisted together to form a single coil I3 I the coil |3| corresponding to the coil |25 of Fig. 3. The coil |3| may be wound on the short tube |21 which is slidably carried on the tube |29 as before.

The constructions sh-own in Figs. 3 and 4 provide nearly unity -coupling between the windings |22 and |38. Close coupling is employed to obtain the highest possible restraining voltage. A high restraining voltage is desirable because it permits the use of a high actua-ting voltage.

One end of the untuned secondary |38 is connected with the grid of the diode-triode tube I8, and the other end is connected to ground through a resistor |39 shunted by a bypass capacitor I4I. The triode section of the tube I8 is connected as an iniinite impedance rectiiier. The triode anode |40 of the tube I8 is connected directly with the B supply conductor |08 and is bypassed to ground by a capacitor |42. The resistor |36 serves as a load resistance for the triode section of the tube I8. This resistor also provides resistance coupling between the triode and diode circuits of the tube I8. The cathode is by-passed to ground through an intermediate frequency bypass capacitor |44. In order to furnish cathode bias voltages the conductor |46 which connects the volume control resistor |34 and the cathode load resistor |36 is connected with the B supply conductor |08 through a resistor |48.

A movable contact |52 operated by the relay armature 12 engages a stationary contact |54 to short out the cathode load resistor |36 when the armature is in its listening position in engagement with the brake disc l68. When the armature is in its tuning position the movable contact |52 engages a stationary contact |56 to connect the conductor |46 with the junction |58 of the secondary winding |38 and the resistor |39 through a resistor |60. When the relay armature 12 is in listening lposition there is a large positive voltage on the cathode of the tube I8 supplied from lead |08 through the resistor |48, while the grid, which is connected to ground through resistor |39, is maintained substantially at ground potential.

When the relay armature is in the tuning position the cathode load resistor |36 is in the circuit. A delay bias for the triode section of the tube I8 is developed by the voltage drop across the resistor |60, which now establishes bias on the grid relative to the cathode by raising the voltage at junction |58 above ground. The current owing from the B supply conductor |08 through the resistor |60 provides delay bias for the triode restraining voltage rectier section of the tube I8.

The grid of the rst audio amplier triode section of the tube 20 is shunted to the cathode by a resistor |62. The grid is connected through a coupling capacitor |64 t-o a movable contact |66 operated by the relay armature 12. When the relay armature is in listening position, the movable contact |66 engages a stationary contact |68 connected with the slider |69 of the volume control |34. When the relay armature 12 is in the tuning position, the movable contact |66 engages a stationary contact |10 connected with the diode plate end of the volume 4control resistor |34 by an interference iiltering resistor |12 and shunted to ground by an interference bypass capacitor |14. Thus different adjustments of the volume control have no effect during tuning.

The tube 22 is connected as a power amplifier. The output transformer 24 has a primary winding |16 which connects the anode of the tube 22 with the B supply conductor I I0. A resistor |15 and a capacitor |11 in series are connected across the primary winding |16.

A series circuit comprising a tone contr-ol capacitor |18 and a variable tone control resistor |00 is connected between the grid of the tube 22 and ground.

The tube 20 has a diode anode |82 which is coupled to the untuned secondary |38 through an intermediate frequency coupling capacitor |84. The anode |82 is connected to ground through a load resistor |86 and to an automatic volume control line conductor |88 through an automatic volume control "filtering resistor |90. A bypass capacitor |92 connects the AVC line |88 to ground. The AVC line is connected with the R. F. amplifier I 9, the iirst detector forming a part of the converter stage I4, and through the I. F. input transformer with the grid of the I. F. pentode I6.

It is advantageous for both listening and tuning to prevent operation of the AVC on weak signals. This may be accomplished by providing a delay bias to prevent operation of the AVC rectiiier at low signal inputs. By this means the full sensitivity of the receiver is available at low signal inputs while at high signal inputs the AVC operates in the usual manner to hold the output at a substantially constant level.

A cathode resistor |94 is connected between the cathode of the diode-triode tube 20 and ground. The cathode is connected through a voltage dividing resistor |96 shunted by a capacitor |98 to the conductor |45 and thence through the resistor |48 to the B supply conductor |08. The voltage drop across the resistor |94 provides an AVC delay bias.

The cathodes of the radio frequency amplifier tube and the rst detector tube are brought out by conductors 209 and 202 which are connected to ground through a vvariable sensitivity control resistor 204 shunted by a bypass capacitor 286. The conductors 200 and 292 are connected with a stationary contact 208 on the relay 10 which is shorted to ground by a movable contact 2|0 when the relay armature 12 is in listening position so that the sensitivity control is effective only during tuning.

In the operation of the receiver, the spring 56 is charged manually to store energy for tuning the receiver. The spring 56 may be charged by manually pushing the knob 48 on the pushrod 46 inwardly. This produces inward movement of the rack 42 and rotates the pinion 54 counterclockwise to tension the coil spring 55. The cores 34, 36 and 38 are carried along with the rack and are moved into their respective coils 94. 28, 3U and 32. During the inward movement of the rack, the pawl 58 ratchets over the teeth of the pinion 54 so that the gear wheel 68 does not have to rotate while the spring is being charged.

The inward movement of the pushrod 46 permits the-spring member 52 t0 close the contacts 88 and S6 of the starting switch 81. Closure of the starting switch energizes the attracting winding 18 of the relay. The relay armature 12 thereby is attracted against the core 82 and the stopping member 68 is released.

The knob t8 is promptly released after it is moved inwardly to charge the spring 56. The spring 50 returns the push-rod 45 and opens the contacts 88 and 68 of the starting switch by overcoming the force of the spring member 92. Except' for the current through the bleeder resistor 91|, the attracting winding 16 is deenergized when the starting switch 81 is opened but the armature 12 is retained in attracted position by residual magnetism, the magnetic field produced by the current passing through the bleeder resistor 64 and the winding 1S, or both.

When the stopping member 68 is released, the spring 56 rotates the pinion 54 and thereby moves the rack 42 forwardly. Since the cores 34, 36 and 38 are moved out of their respective coils, the receiver is tuned toward the high frequency end of the tuning range.

When the pinion 55 is being rotated by the torsional spring 56, the pawl 58 forms a positive driving connection between the pinion 54 and the gear 68. Consequently the pinion 511 drives the entire gear train, comprising the gear '66, the pinion 62, the gear 64, the pinion 66, the stopping member 68, and the wind vane 69. The Wind vane controls and stabilizes the tuning speed by providing rapidly increasing resistance to the rotation of the stopping member 68 as the speed of the wind vane increases. Because of the high gear ratio between the pinion 54 and the stopping member 68, the wind vane rotates at a considerable speed during tuning and the speed regulation produced by the small wind vane isquite eiective.

As indicated above, the spring 56 may be initially tensioned or loaded by twisting the collar 65 with respect to the shaft 51 and the pinion 54. The spring is initially loaded to such an extent that the change in the tension of the spring, caused by the movement of the rack i2k over its entire range, is relatively small with respect to the initial tensioning. Consequently the torque exerted by the spring upon the pinion 54 is relatively constant over the entire range of motionof the pinion and the rack. This constructional feature provides adequate torque or force for starting and running the tuner over the entire tuning range, with a minimum force and movement required forrecharging the spring and a minimum restraining force for regulating the speed.

When a signal of suiiicient strength is tuned in, the tube I8 produces an operating voltage impulse across the volume control resistor ld. The exact manner in which the impulse is produced will be discussed Vin detail below. The impulse is transmitted to the grid of the iirst audio triode section of the tube 25 through the interference filtering resistor W2, the contacts |10 and |66, and the coupling capacitor |64.

The impulse isamplied by the first audio triode and 'the poweramplier tube 22y and is supplied to the relay releasing winding Si! by the secondary |65 of the `outputA transformer 24.' This operating voltage impulse is of relatively low frequency and, therefore; it is desirable that the output transformer be constructed to provide effective power output at low frequencies. For similar reasons, the coupling capacitor 2| should have sufficient capacitance. The resistor |15 and the capacitor |11 are provided to improve the sensitivity and to promote proper relay action.

The secondary |65 of the output transformer 24 and the releasing winding 86 are polarized with respect to the attracting winding 18 so that the iirst signal impulse through the releasing winding bucks the residual magnetism and the magnetism produced by the current through the attracting winding and the bleeder resistor 94. As

previously stated, residual magnetism or bleeder current may be utilized separately or together to latch the relay armature in its tuning position. If the impulse in the releasing winding is of sufcient strength, the relay armature 12 is released and tuning is discontinued by engagement of the armature with the brake disc or stopping member 66.

The magnitude of the holding current through the bleeder resistor 94 is one of the factors determining the sensitivity of the relay 10. The sensitivity generally is increased if the bleeder current is decreased. The retentivity of the core 82, the armature 12 and the frame 84, as Well as the strength or adjustment of the armature spring 15, also ailect the sensitivity.

The adjustment of the sensitivity control resistor 26:1 determines the strength of the signal necessary for stopping the tuning of the receiver on a signal. The operation of the tuning mechanism is not affectedfby the setting of the volume control resistor |34 because the slider |69 of the volume control is disconnected during tuning, and the signal output is taken through the interference filtering resistor |12 from the end of the volume control resistor connected with the diode anode |36. During tuning, the resistor |12 and the capacitor |14 `provide additional filtering to minimize the possibility of the tuner being stopped by static or other interference. This filter does not appreciably aiect the audio response during listening.

When the relay armature 12 has been released to stop the tuning, the movable relay contacts shift to their listening position The movable contact 2 |6 shorts out the sensitivity control resistor2il4 so that the full sensitivity of the receiver controlled by the AVC is available for listening.

During listening the movable contact |52 shorts out thefcathode load resistor |36 to prevent any' signal voltages from developing across this re-;`

sistor, and to permit the full signal voltage to develop across the volume control resistor |34.

The triode section of the tube |8 is cut 01T by distrode restraining voltage rectifier with the strongest signal input.

For listening, the movable contact |66 con-l nects the input of the rst audio tube 20 to'the slider. |66 Aof the volume control resistor sothat the slider may be adjusted to vary the volume.

It will be seen that both the tuning and the listening signals come from the same diode plate i3@ and also from' the same tuned circuit-consistlng of the secondary winding |26 and the capacil' -tor |28. For tuning, the signal from the diode section of the tube I8 follows the path through the interference filter resistor |12, but, for listening, the signal passes through the volume control resistor |34 and the slider |69, as determined by the position of the switch contact |66. As a result, the last tuned circuit which establishes the frequency for signal tuning is also the last tuned circuit which establishes the frequency of the signal during listening. During tuning, the width of the response of this tuned circuit is narrowed by the restraining voltage, particularly to strong signals. However, the center frequency is the same as during listening. This arrangement eliminates any possible error in tuning which might occur if different tuned circuits were employed for tuning and listening, since one of the circuits could get out of tune with respect to the other.

The .operation of the signal tuning circuits will now be described in detail. As stated above, the coupling between the primary winding |22 and the tuned secondary |25 may be adjusted by moving one of the coils to increase or decrease the axial distance between them. A degree of coupling between these coils which gives very good results may be secured in the following manner.

First, the delay bias on the restraining voltage rectier is reduced to zero by adjusting the gridcathode bias of the tube I8 to the value which is just sufficient to produce plate current cut-off in the triode with zero signal input. The gridcathode bias may be adjusted by varying the relative values of the resistors |39 and |60. Then a signal of moderate strength is supplied to the receiver. The signal may be derived from a signal generator operating at the central intermediate frequency and may be applied, for example, to the grid of the intermediate frequency amplifier' tube |6. The coupling between the primary |22 and the secondary |26 is then adjusted so that there is an appreciable voltage output from the actuating voltage diode rectier section of the tube I8, measured, for instance, across the volume control resistor |34. The coupling is then reduced until this measured voltage substantially disappears. At this point the restraining voltage developed by the triode section of the tube |8 across the cathode resistor |36, and applied to the diode plate 30 through the volume control resistor, is substantially equal to the peak I. F. actuating voltage applied to the plate |30 by the coil |26.

Next, the relative values of the resistors |3t and are changed to increase the voltage between the cathode and the grid of the tube I8 to provide a delay bias. The amount of delay bias that should be used Will be discussed below. The receiver is now adjusted for its normal operation. If the delay bias were not provided, the restraining voltage developed by the triode section of the tube I8 would always bias the diode section of the tube so that it would pass substantially no current during tuning. With the additional delay bias applied to the restraining voltage triode rectifier, an operating voltage appears across the volume control resistor |34 whenever a signal is supplied to the transformer |20.

If the strength of the applied signal increases from zero, the operating voltage across the resistor |34 increases from zero until the peak voltage developed across the untuned winding |38 approximately equals the delay bias. Up to this point the delay bias prevents the restraining voltage rectifier from conducting. Any further increase in the applied signal strength does not substantially increase the operating voltage developed across the resistor |34 because the restraining voltage developed across the cathode resistor |36 increases the bias on the diode plateV |30 approximately as fast as the voltage devel-- oped across the winding |26 increases. The restraining voltage thus prevents any further substantial increase in the operating voltage. Thus strong signals do not produce substantially greater operating voltages than weaker signals.. For this reason both strong and weak signalsare tuned closely to the center intermediate fre-A quency, and the effective width of a signal interms of frequency does not increase substantially with increasing signal strength.

Thus the operating voltage increases toward a maximum value which does not greatly exceed'y the value produced by a signal which is just sufficient to overcome the delay bias. This maxi-- mum operating voltage depends upon the value of the delay bias, and is of the same order as the delay bias. Raising the delay bias increases the maximum operating voltage, and vice versa..

In tuning through a station, the operating voltage rises to a peak at the center intermediate frequency. The operating voltage must attainy or exceed a predetermined value in order to stop` the tuning of the receiver. The minimum oper- C ating voltage that will stop the tuning mechanism may be termed the operating level. A station, when tuned in, stops the tuning mechanism or not according to whether or not the operating signal produced across the resistor |34 exceeds or at least reaches the operating level. The magnitude of the operating level depends upon the sensitivity of the relay and the amount of amplification between the resistor |34 and the relay.

The delay bias should be great enough to provide a maximum operating voltage which equals or exceeds the operating level. It is desirable to stop the tuning of a station near the center of the channel which the station occupies.

Consequently the operating voltage produced by a station signal preferably should exceed the operating level near the peak of the operatingTv voltage. This should be the case for relatively strong as well as relatively weak stations. For

g this reason the maximum operating voltage preferably should not greatly exceed the operating level. If the maximum operating voltage is raised too high with respect to the operating level, the tuner will tend to stop on strong signals before the receiver is correctly tuned. Moreover, the tuner will tend to stop twice or more on strong signals when the starting switch is operated, instead of moving on to the next station.

The strength a received signal must have to produce an operating voltage at least equal to the operating level depends upon the setting of the sensitivity control resistor 20. Thus the sensitivity control may be adjusted so that a greater or smaller number of stations will stop the tuning. With a setting of the sensitivity control providing high gain in the R. F. and I. F. stages, relatively Weak as well as relatively strong stations will be signal tuned. Progressively reducing the gain will prevent signal tuning of progressively more stations which are then too Weak to produce operating voltages at least as great as the operating level.

The relationship of the operating level and the delay bias may be such that signals may be received which will stop the tuning but fail to overcome the delay bias. If the spring driven tuning mechanism of the receiver tunes in such a signal, the triode section of the tube I8 does not conduct, and a restraining voltage is not produced. As such a signal enters the frequency band to which the tuned winding |26 responds, a voltage begins to develop across the winding |26. This Voltage is rectified by the diode section of the tube I8 and produces an operating signal across the volume control resistor |34. After the signal reaches the operating level, the tuning is stopped near the center intermediate irequency. This assumes that the signal must develop nearly its peak voltage before it reaches the operating level.

A restraining voltage is produced by signals which are suiiiciently strong to overcome the delay bias. As soon as a restraining voltage is produced it biases the diode plate |36 and thereby tends to reduce the output of the diode so that the operating voltage across the resistor |34 tends to exceed the operating level nearer the center intermediate frequency than Would be the case Without the restraining voltage. Consequently the restraining voltage has a narrowing eiiect, in terms of frequency, onthe signal tuning action. The restraining voltage improves the tuning accuracy and tends to prevent stopping before the center I. F.- frequency is reached and stopping more than once on a station, especially on strong signals.

The tuning response characteristic of the untuned secondary winding |38 is like that of the primary |22 and is somewhat broader than the i response characteristic of the secondary tuned circuit comprising the winding |26 and the capacitor |28. The response of the untuned circuit should not be narrower and preferably should be wider than that of the tuned circuit.

If the spring driven tuning mechanism tunes in a signal having a strength suiiiciently exceeding the value required to overcome the delay bias, a restraining voltage is produced which tends Ato narrow the response of the diode actuating rectilier. As such a strong signal, applied to the transformer |26, approaches the center intermediate frequency, a substantial voltage develops across the untuned secondary |38 before any substantial voltage develops across the Ituned secondary |26. Such a strong signal developing across the untuned secondary |38 overcomes the delay bias before any substantial voltage develops across the tuned secondary |26. When the delay bias has been overcome, the triode section of the tube |8 develops a restraining voltage across the cathode resistor |36. This voltage biases the diode plate |30 negatively with respect to the cathode of the tube I8 and thus restrains conduction in the diode section un-til the peak voltage developed by the tuned secondary winding |26 exceeds the restraining voltage.

Once a voltage starts tokdevelop across the tuned secondary |26 it rises at a more rapid rate than the voltage across the untuned secondary 138, due to the steeper slope of its voltage versus frequency response. When the signal applied to the transformer closely approaches the center intermediate frequency, the voltage across the tuned secondary |26 begins to exceed the restraining voltage and the diode section of the tube I8 begins to conduct. This produces an operating impulse across the volume control resistor |34 for stopping the tuning mechanism 1n the manner described above.

If the restraining voltage were not provided, a strong signal would produce an impulse of suicient strength to stop the tuning mechanism at a frequency farther removed from the center intermediate frequency than in the case of a weak signal. It will be apparent that the restraining voltage prevents strong stations from producing a, tuning signal higher and wider than produced by weaker stations. Together with the delay bias the restraining voltage provides relatively uniform response of the actuating circuit to signals of varying magnitude.

The iiux latched relay may be adjusted to be particularly sensitive and the audio amplifying system provides relatively great amplification of the operating signals. As a result, the operating level may be made quite low. Less than one volt of operating voltage may be employed. In such a case the delay bias'on the restraining voltage rectifier may be in the order of two or three volts. This provides a narrower operating voltage signal. However, if a larger operating voltage is employed, the operating level can be made higher by adjusting the relay for lower sensitivity or employing less gain in the relay amplifier. With a less sensitive relay arrangement the operating level may be raised. In this case the delay bias on the restraining voltage rectifier may be increased and the maximum operating voltage raised thereby. For the reasons explained previously, Ithe maximum operating voltage should be greater than but comparable with the operating level. When the delay bias is raised, the variation of the operating voltage with changing signal strength will be greater for signals of insuiiicient strength to overcome Ithe delay bias. With an increased delay bias there will be more diiierence between strong signals and relatively weaker signals which are insufficiently strong to overcome the delay bias.

For best operation the weakest desired station signals should produce adequate I. F. actuating voltage in the tuned winding |26. The highest I. F. actuating voltage is produced when the spacing between the primary |22 and the tuned secondary |26 is adjusted to provide approximately optimum coupling. However, to avoid broad tuning on strong signals, suiiicient restraining voltage should also be provided. The arrangement of Fig. 1 provides a high restraining voltage because of the large number of turns in the untuned secondary |38 and its tight coupling to the primary |22. This may be done when an infinite impedance triode rectifier is employed to obtain the restraining voltage. The load imposed upon the secondary |38 by the iniinite impedance rectiiier is very low. Consequently the secondary |38 may be coupled very closely to the primary |22 without appreciable loss of voltage due to loading of the primary.

To produce the highest actuating voltage, the resistor |34 should have a high value relative to the resistor |36. However, the resistor |36 must have a great enough value to supply suiicient restraining voltage.

The great mechanical advantage provided by the gear train between the stopping member 68 and the pinion 54 increases the effectiveness and accuracy of the braking action of the armature 'I2 when it engages the stopping member 68. Thus excessive tension is not required of the spring '14.

Very positive holding of the stopping member can also be had by providing the stopping mem-.

berwith` teeth, `and the.` armature with an abutment to engagetne teeth. However, the teeth must be spaced so that the distance between adjacent teeth is small enough so Ithat it has no important effect on the tuning.

When a different station is desired, the starting switch 81 is `closed momentarily by tapping the knob 4B. The relay winding 13 is energized and the armature 12 is attracted into its tuning position. Thus the stopping member Si? is released. The spring 56 drives the tuning mechanism until another signal of sumcient strength is tuned in, or until .the high 'frequency end of the tuning range is reached. If a signal is tuned in, the relay armature 12 is released to the movement of the stopping member 60.

When the high frequency end of the tuning range is reached, the spring 56 is recharged by manually pushing the knob 48 inwardly. Recharging is not required frequently since several stations spaced across the tuning range will ordinarily have suiiicient strength for signal tuning in most localities.

The spring 56 may be partially recharged at any time in order to tune in a particular station, for example. The amount the tuning cores are moved and the amount the spring is recharged are determined by the extent of the inward movement of the control knob. The knob may be pushed in to move the tuner to the low frequency side of a desired station, and the station may be tuned in by tapping the control knob. The receiver dial may be observed during this procedure to establish visually the position of the desired station.

Fig. 5 illustrates the external appearance of the receiver. The pushrod cr control plunger 46 protrudes through a panel 2|0 enclosing the front of the receiver. A tuning dial or scale 2&2 having an indicator 2| 4 is positioned immediately below the pushrod 46. The volume control resistor |34 and the battery switch 85 may be controlled by aknob 2 I8, and the tone control resistor |80 may be controlled by a ring 2|6. The sensitivity control may be controlled by a knob 2|1 and the receiver may be conditioned for manual or signal tuning by means of a lever '2|9. The receiver may be enclosed in a housing 220 and may be adapted for mounting on the dash of an automobile.

The above mentioned application of Edward F. Andrews, Serial No. 195,161, should be consulted for a description of further mechanical features of the receiver. For example, this copending application contains a description of the linkage by which the rack 42 operates the dial indicator 2M and the mechanism for manual tuning which is controlled by the lever 2|0.

Fig. 6 illustrates a signal tuned receiver which is dilerent in some respects from the receiver of Figs. '1-5. The modifications embodied in the receiver of Fig. 6 will now be described in detail. In other respects the receiver may be similar to the receiver of Figs. 1-5.

In the receiver of Fig. 6, an additional triode 250 is used for stopping the tuning mechanism on a signal instead of employing the audio amplifying system for this purpose. In this modied receiver it is unnecessary to change the volume control connections for tuning. Consequently the switch contacts |66, |68 and |10 are omitted and the grid of the audio amplier tube is connected directly to the slider |69 of the volume control resistor |34 through the blocking capacitor |64. The tube 250 may be a high trans- `1.6 conductance pentode such as a GAUG connected as a triode.

The relay 'l0 is provided with a windngf252. which replaces the windings 18 and 80. The winding 252 is connected between the anode of the tube 250 and the B-lconductor |08. Since the winding 252 is controlled by the plate current in the tube 250, the winding hasv a considerably greater number of turns than either of the windings 10 and 80 of the receiver of Fig. 1. The relay 10 of Fig. 6 has a soft iron core 253 having the smallest obtainable retentivity, unlike the liux latched relay of Fig. 1. The armature 12 is also made of soft iron.

The grid of the relay operating tube'250 is connected by a conductor 254 to the junction ofr the resistor |12 and the capacitor |14.. The lower end of the volume control resistor |34 is connected to the cathode of the tube I8. The cathode of the relay operating tube 250 is connected through a resistor 256 in series with a resistor 251 to the junction conductor |46 and thence through the cathode resistor |36 to the cathode of the tube I8. Cathode bias for the tube 250 is provided by the resistors 256. and 251 as well as a resistor 258 connected between the cathode and the B-lconductor |08.

The starting switch 81 is connected in series with a resistor 260 between the plate of the tube 250 and ground.

The switch contacts |00 and |04 are utilized in this receiver but they are connected differently than in the receiver of Fig. 1. The contact |02 is omitted. The movable contact |00 is connected to one end of the resistor 251 and the contact 204 to the other end, so that during tuning the resistor 251 is shorted out.

The contacts 208 and 2|0 are connected the same as in Fig. 1 so that during listening they Short out the sensitivity control resistor 204. The speaker 26 is connected directly across the output transformer secondary |05, one terminal of the secondary being grounded. During tuning the speaker is shorted out because the grounded movable contact 2|0 engages a stationary contact 26| connected to the ungrounded Side of the speaker.

Since the tuning impulses are transmitted to the relay by the tube 250 rather than by the audio amplifying system, it is not so important that the amplifying system have an adequate low frequency response.

The distinctive features of the operation of the receiver of Fig. 6 will now be explained. It will be assumed that initially the spring 56 is at least partly charged and the tuning is stopped on a signal. The relay armature 12 then is engaged with the stopping member E8 and the relay contacts are in their listening positions.

A current ilowing from the B supply conductor 00 through the bleeder resistor 258 and the cathode resistors 256 and 251 produces a voltage drop across the resistors which is suflicient to bias the tube 250 far beyond cut-off. Consequently, no plate current flows in the tube during listening regardless of any signals impressed on its grid :from the conductor 254.

When a new station is desired7 the starting switch 01 is closed momentarily by tapping the knob 48 in the same manner as in the receiver of Fig. 1. When the starting switch is closed, a current ows from the B supply conductor 08 through the relay winding 252, the resistor 260 and the starting switch to ground. The magnetic ux :produced by the currentis sufficiently strong .to at- 17. tract the relay armature 12 into its tuning position out of engagement with the stopping member 68.

The armature moves the relay contacts to their tuning positions and the contacts and |04 short out the resistor 251. The grid-cathode 'bias on the .tube 25|) thereby is reduced to such an extent that plate current flows in the tube, assuming that an operating signal is not being developedl The plate current of the tube 250 passes through the relay Winding 252. The plate-current through the tube is sufficient to hold the relay armature 12 in attracted position when the starting switch 81 is opened.

When a signal of suicient strength is tuned in, an operating signal is developed across the series circuit of the volume control resistor |34 and the cathode resistor |36 and is impressed upon the grid of the tube 250 by the resistor |12 and the conductor 254. If the operating signal` on the grid of the tube 250 has sufficient strength, it reduces the plate current through the relay winding 252 to such an extent that the relay armature 12 is moved to its listening position by the spring 14. The relay armature engages the stopping member 68 and stops the tuning mechanism on lthe signal- The relay of Fig. 6 is different .from the ux latched relay of Fig. 1. Among other things, the magnetic circuit of the relay of Fig. 6 is made of soft relay iron in order to minimize residual flux. The relay of Fig. 6 also may have an air gap between the armature and the core when the former is in attracted position.

In the receiver of Fig. 6 the actuating voltage is developed across the volume control resistor |34and the restraining voltage, across the cathoderesistor |36. The ends of the resistors |34 and |36, having positive operating polarity, are connected together so that the restraining voltage bucks the actuating voltage. The resultant operating voltage across the resistors in series is applied between the grid and the cathode of the relay tube 250. The grid is connected through the resistor |12 to the negative end of the volume control resistor so that the plate current in the tube is reduced when the actuating voltage exceeds the restraining voltage. If the plate current is reduced sufficiently, the relay armature 12 is released and thetuning is stopped.

The operating level depends upon the sensitivity of the relay 1|) and the amount of amplification provided by the relay tube 256. The operating level is likely to be higher than in the receiver of Fig. l because the sensitivity of the relay of-Fig. 6 may be less than that of the flux latched relay of Fig. l, and because the single relay tube may provide less gain than the audio system used in the relay amplier in Fig. 1.

When the operating voltage is derived from the restraining and actuating voltages connected in series, both positive and negative voltages are present in the operating output from the two rectiers. However, with the relay and relay tube system shown in Fig. 6, only the negative coml ponent in excess of the positive component can 18 be noted that the operating or resultant voltage develops across the resistors |34 and |36 connected in series opposition instead of across the resistor |34 'by itself. Therefore, in this embodiment the effective operating voltage should be measured across the resistors |34 and |36 in series. With no signal the voltage at this point is zero. With a moderate signal applied as in Fig. l a voltage appears across these resistors. When the adjustment of the coupling is being made, the delay bias should be removed from the restraining voltage rectifier as described in relation to Fig. l. The coupling is then adjusted with the input signal still present so that the voltage across the two resistors is substantially zero. This shows that the restraining voltage is now equal to the actuating voltage and has neutralized it. When the delay bias is restored, the same input signal will again produce a voltage across these two resistors. The voltage remains substantially constant with increasing signal strength for signals .having sufficient strength to overcome the delay bias.

The series arrangement of the resistor across which the actuating and restraining voltages develop, as shown in Fig. 6, may be advantageous Where a single triode is employed vbetween the relay and the source lof the operating voltage, as here shown. Where the outputs of the restraining and actuating voltage rectiers are connected in series opposition, as in Fig. 6, a somewhat higher operating voltage may be obtained than with certain arrangements where the restraining voltage rectifier biases the actuating voltage rectifier. This may be of some advantage where a less sensitive relay system having a higher operating level is employed, as in Fig. 6. With the higher operating level of Fig. 6 a correspondingly higher delay 'bias preferably is employed so that the restraining voltage develops in response to any signal exceeding the operating level by a small margin. This relation between the operating level and the delay bias is generally desirable.

Fig. 7 illustrates a modied signal tuned receiver. The differences between the receiver of Fig. 7 and the receiver of Fig. 1 will now be described. In other respects the receiver of Fig. '7 may be similar to the receiver of Fig. l.

In the receiver of Fig. '7 a crystal rectier 300 is employed as a signal detector for listening and as the actuating voltage rectier for signal tuning. The diode plate of the tube 20 is employed to obtain the restraining voltage as well as the automatic volume control voltage. Consequently the tube |8 is omitted from the receiver of Fig. 7.

The crystal rectifier 300 may be of the germanium crystal type. A series circuit comprising the crystal rectier 300, a junction conductor 30|, the volume control resistor |34 and the intermediate frequency ltering resistor |32 is connected across the terminals of the secondary tuned circuit comprising the transformer winding |26 and the capacitor |28. The volum'e control resistor is shunted for intermediate frequencies by a bypass capacitor 302. As in Fig. 1, the by-pass capacitor |31 is connected between one end of the winding |26 and ground.

One end of the untuned secondary winding |38 is connected to the diode plate- |82 of the tube 20 and the other end is connected to a junction conductor 304. The conductor 304 is connected through a load resistor 306 to ground, the `load resistor being shunted by an intermediate` frequency bypass capacitor 308.' The conductor 364 is also connected to the automatic volumecontrol line 188 by the filtering resist-or I 511i. A delay bias between the cathode of the tube 211 and the diode plate 132 is produced by three resistors 316, 312 and 311i, connected in series between the cathode of the tube and ground, together with a bleeder resistor 313 connected between the B supply conductor li'il and the cathode.

All of the relay switch contacts S9 are employed in the receiver of Fig. 7 but some of them are connected dinerently than in the receiver of Fig. 1. The movable contact 152 is connected to the junction conductor 3111 between the crystal rectier 3D0 and the kvolume control resistor' 1311. When the relay contact 152 is in its listening position it engages the movable contact 1513 which is connected to ground. When the movable contact 152 is in its tuning position it engages the contact S which is connected to the junction conductor 3611 and thus to ground through the load resistor 306.

The movable contact 13G is connected directly to the grid oi the triode section of the tube 20. In its listening position the contact 166 engages the contact itt which is connected through the blocking capacitor 131i to the slider 163 of the volume control resistor 134. The Contact 153 is also connected through a grid return resistor 3211 to the junction of the cathode resistors 313 and 312. In its tuning position the movable contact 166 engages the stationary contact 1111 which is connected through a blocking capacitor 322 and the interference filtering resistor 1'12 to the junction of the resistor |32 and the volume control resistor 134. The interference bypassing capacitor 1111 is connected between the junction of the resistor 112 and the capacitor 322 and ground. The contact 1`11l is also connected through a grid return resistor 3261 to the junction of cathode resistors 312 and 31111. The connections to the contacts 133, 162, 1111i, Edt and 213 are the same as in Fig. 1.

As in Fig. l, `the anode of the triode section of the tube 2) is connected through the coupling capacitor 21 yto the grid `of the second audio amplier tube 22.

In the receiver ci Fig. '.7 the transformer 120 is ordinarily constructed somewhat differently than in Fig. 1. As in the receiver of Fig. 1, the untuned secondary Winding 138 is coupled as closely as possible to the primary winding |22 in order to secure the maximum `obtainable restraining voltage. In the receiver of Fig. 7 the restraining voltage rectifier is a diode and not an infinite impedance rectier employing a triode. Consequently the restraining voltage rectiner imposes an appreciable loading effect upon the secondary winding 138. In order to avoid excessive loading of the primary winding 122, the untuned secondary winding 138 ordinarily has a smaller number of turns than the primary winding in the receiver `of Fig. '7.

In order to secure amaximum obtainable coupling between the primary winding 122 and the untuned secondary winding 13S, the two windings may be formed as one coil. The windings may be wound from separate wires laid side by side or twisted together until the secondary winding |38 is completed. Then the end of the secondary winding may be anchored and brought outand the remaining turns of the primary winding may be wound to complete the coil.

The receiver may be modied to employ capacie tance-resistance coupling between rtheV primary |22 and the restraining voltage recter instead of inductive coupling. However, such capacitance-resistance coupling can be expected to provide somewhat less restraining voltage than the inductive coupling, and so the inductive coupling is generally preferable.

In the receiver of Fig. 7 the load` resistors of the actuating voltage rectifier and the Yrestraining voltage rectifier are connected in .series opposition during signal tuning. The end ci one resistor is connected to the end of the other resistor having like operating polarity so that the outputs oi the rectiiiers buck each other. The scheme exemplied by Fig. 1 of utilizing the restraining voltage to bias the actuating voltage rectifier is not employed in Fig. 7 because ordi nary crystal rectiers mayv not give satisfactory operation with a reversely polarized biasing voltage.

The restraining voltage develops across the load resistor 306 and the actuating voltage develops across the volume control resistor 134. The operating voltage which is the resultant. of combining the actuating and restraining voltages, develops across the resistors 3115 and 1311 in series. When the relay contacts 99 are in their tuning position, the resistors 134 and 3BG are connected in series by the contacts 152 and 156. The operating voltage impulse is transmitted to the grid of the triodesection of the tube 21) along a path includingthe interference filtering resistor 1'12, thecapacitor 322, and the contacts and 166. During tuning the resistor 324 serves as a grid return resistor. Consequently the voltage drop across the resistors 310 and 312 biases the grid of the tube 20 with respect to the cathode. This voltage is suilicient .to bias the triode section of tube 2li toward or to cut-oi. Consequently the triode responds effectively to only the positively polarized portions of the signal impressed on its grid during tuning. This biasing is desirable so that a tuning impulse is transmitted to the relay 10 only when the actuating voltage across the volume control resistor |34 exceeds the restraining voltage across the load resistor 306. The crystal is polarized to produce a positive actuating signal upon the grid of the tube 20, while the diode section of the tube 20 is polarized to produce a negative restraining voltage.

In order to prevent the negative restraining voltage from producing `spurious positively polarized signals on the grid of the tube 20, the capacitor 322, and the resistor 324 should be suiciently largeso that the impulse signals produced during tuning aretransrnitted to thegrid Without substantial spurious reversals of polarity.

`During signal tuning, the voltage drop across the resistors 310, 312 and 314 produces a delay bias on the diode section of the tube 2U. The diode acts as the restraining voltage rectifier. A suitable delay bias vmaybe arrived at in accordance with the considerations pointed out in the description of the receiver of Fig. 1. The coupling between the primary 122 and the tuned secondary 126 maybe adjusted in substantially the samemanner described in connection with the receiver of Fig. 6. Impulses for stopping the tuning mechanism are produced in much lthe same manner as in the receiver of Fig. 1. However, the restraining voltage is connected to buck or neutralize the actuating voltage rather than to bias the actuating voltage rectifier as in Fig. l. Tuning signals representing the combination -of the actuating and restraining voltages are supplied to the grid of the tube 2D. VThese tuning signalshave an excess of the positively polarized Vwhich latches the relay armature 12.

sistor |32 to a junction conductor 366.

actuating voltage over they negative restraining voltage. During tuning the triode section ofthe tube 20 is biased to or nearly to cut-off so that only the positive components can produce eiiective plate current in the triode and thereby stop kthe tuning mechanism.

As in the receiver of Fig. 1, the relay winding applied to the winding 80 by the output transformer secondary |05, tends to buck the ux However, in thereceiver of Fig. 7, the relative polarity of the winding 80 and the output transformer secondary is the reverse of the polarity in the receiver of Fig. 1. This is true because posisively polarized tuner stopping impulses are applied to the grid of the tube in the receiver of Fig. 7 instead of 4the negatively polarized impulses applied to the grid in the receiver of Fig. 1.

In Fig. 7 the grid of the first audio triode in the tube 20 is biased at or-near cut-off during tuning to prevent it from responding to the negative restraining voltage. This biasing raises the operating level, but the operating voltage is also relatively high because of the series connection of the restraining and actuating Voltage rectifiers. In any event, adjustment of the operating level can be eiected by adjusting the bleeder current, the tension of the relay spring 14, or both. j

When the relay contacts 99 are in their listening position, Vthe circuit including the crystal rectier 300 operates as the signal detector. The junction conductor connected with one end of the volume control |34 is grounded by the contacts |52 and |54. Signals are transmitted from the slider |69 ofthe volume control resistor to the triode grid of the tube 20 through the capacitor |64 and the contacts |68 and |66. For listening, the resistor 320 is the grid return resistor. Consequently. only the drop across the resistor 3|0 is impressed between the grid and the cathode. This drop provides the usual bias for utilizing the triode section of the tube 20 as an audio amplifier. y

'During listening, ,the restraining voltage has no effect since the load resistor 306 for the restraining Voltage rectiiier is disconnected by the contacts |52 and |56 from the crystal rectier circuit.

The contacts |00, |02, |04, 208 and 2|0 operate in the same manner as in the receiver of Fig. 1.

The differences between the modied receiver of Fig-8 and the receiver of Fig. 1 will now be described. In other respects the receiver of Fig.

8 may be similar to the receiver of Fig. 1.

'In the receiver of Fig. 8 the tubes I8 and 20 are replaced by a single tube 350 having an independent dode section 352 and a diode triode section' 354 having a diode plate 356, a triode grid 358, a triode plate 360 and a common cathode 362. for the diode plate 356 and the triode section. The` independent diode 352 has a separate .cathode 353.

One side of the tuned secondary winding |26 is connected to the plate 0f the independent diode 352 and the other side of the winding is connected toa junction conductor 364. The cathode of the independent diode 352 is connected through the intermediate frequency filteringre- The junction conductor 366 is connected through a .load-resistor 368 .to ground. The ends of the n1- tering resistor |32 are bypassed to ground for intermediate frequencies by the bypass capacitors The movable relay contact |66 is grounded.

. In its listening position the contact |66 engages the contact |68 which is connected to one side of the volume control resistor |34. The other side of the volume control resistor is connected to the junction conductor 366. The contact |10 is omitted from the receiver of Fig. 8.

'I'he slider |69 of the volume control resistor |34 is connected through the blocking capacitor |64 to the grid 358 of the triode section of the tube 350. The anode 360 of the triode section is connected through the coupling capacitor 2| to the grid of the second audio tube 22.

One side of the untuned secondary winding |38 is connected to the diode plate 356, and the other side is connected to a junction conductor 310 which is bypassed to ground for intermediate frequencies by a capacitor 312. The junction conductor 310 is connected through an intermediate bypassed to ground for intermediate frequencies by a capacitor 316. The junction conductor 364 is connected through a load resistor 318 to ground. A source of delay bias may be connected between terminals 380 and 382, respectively connected to the cathode 362 of the tube 350 and ground. The source is indicated by a dotted line between the terminals in Fig. 8. The delay bias source may be a battery, a suitable power supply, or a resistor having a suitable voltage drop across its terminals. For example, a delay bias may be obtained by a circuit similar to the arrangement of Fig. 1 in which the drop across the resistor |60 furnishes the delay bias.

In the receiver of Fig. 8 the movable relay contact |52 is grounded. In its listening position, the movable contact |52 grounds the contact |54 which is connected to the junction conductor 364. The contacts |00, |02, |04, 208 and 2|0 are connected in the same manner as in Fig. 1.`

In the receiver of Fig. 8 the diode `plate 356 and thecathode 362 function as the restraining voltage rectier. Consequently the restraining voltage rectifier imposes an appreciable load upon the untuned secondary winding |38. In order to avoid loading thel primary winding |22 excessively, the secondary winding |38 ordinarily will have a smaller number of turns than the primary winding. The windings |22 and |38 may be `giound as one coil as described in connection with In the receiver of Fig. 8 the independent diode 352 is the actuatingA voltage rectifier and the diode comprising the plate 356 and the cathode 362 is the restraining voltage rectifier. During signal tuning the operating Voltage develops across the output resistor 368 of the actuating voltage rectiiier and the restraining voltage develops across the load resistor 318. When the relay contacts 99 are in their tuning position, the contact |54 is disconnected from ground and the restraining voltage is impressed upon the plate of the independent diode 352 through the secondary winding |26. The restraining voltage is negatively polarized so that it tends to restrainrectiiication by the diode 352.

The operating voltage impulse for stopping the tuning mechanism is transmitted from the junction conductor 366 to the grid 358 of the tube 350 through the volume control resistor |34 and the capacitor |64. During signal tuning the vol- `accaaoc 23 .ume control resistor is disconnected from ground `by thecontacts |66 `and |66 so that the position of the volume control slider |69 has no effect upon the magnitude of the tuner stopping impulse.

.'Ihe delay bias on the restraining voltagerectifier land .the coupling between the primary |22 .and the tuned secondary |25 may be :adjustedin the'manner described in connection with the receiver of Fig. l. Consequently atuning impulse is produced in the` receiver of Fig, 8 in essentially the same manner as in thereceiver of Fig. l. The use of an independent diode with separate .cathode for the actuating voltage rectifier `in a single tube also containing a diode triode is a distinguishing feature of the receiver of Fig. 8 over-the receiver of Fig. l. Moreover, thesame independent diode produces a positive detector listening signal as well as a positive actuating voltage.

VAs iri Fig. l, the same tuned circuit, comprising the winding |26 and the capacitor |28, and the same rectifier 352, produce the vactuating' voltage during tuning and the detector voltage during listening. In Fig. 8 both theV actuating voltage and the detector voltage havepositive polarity, while in Fig. 1 both havenegative po l-arity.

l While I have shown and described several preferred embodiments of my invention, vit will be apparent that numerous variations and modifications -thereof may be made without departing from the underlying principles of the invention. I therefore desire, by the following claims, t include Within the Vscope of the invention all such variations and modications by which substantially the results of my invention may be obtained through the use of substantially the same .or equivalent means.

I claim:

1. In signal tuned radio apparatus, variable tuning means, means for varying said tuning means, means for stopping the variation of said tuning means in response to an operating voltage tuned by said tuning means, a circuit coupled to receive signal voltage from said appa.- ratus, a rst rectier lcoupled to said circuit, a tuned circuit coupled to receive signal voltage from said apparatus, a second rectifier coupled to Asaid tuned circuit,means for deriving a 'voltage 'from the rst rectier and applying it as a 'bias Vto an element of said second rectifier toreduce the output of the second re'ctier, means :to prevent rectication of said rst rectifier .in

response to signal voltage below a predetermined value, and means coupling said second .rectifier to vsaid stopping means.

2. In signal `tuned radio apparatus,` variable tuning means, means for varying said tuning means, means for stopping the variation of said tuning means in response to an operating voltage tuned by said tuning means, a circuit cou- Vpled to receive signal voltage from said apparatus, a high impedance triode rectier coupled rto .said circuit, a tuned circuit coupled .to receive signal voltage from said apparatus, a second rectier coupled. to said ltuned circuit, means interconnecting sad two rectiers wherebythe effective output of the second yrectiiier is reduced by the operation of the high impedance triode rectiiier, and means coupling said `second .rectier to said stopping means.

3. In signal tuned radio apparatus, variable tuning means, means for varying said .tuning means, means. for .stopping the variationvofisadd tuning means response toan operating. ivolt age tuned by .saidftuningv means, a circuit :c011- pled to receive `signalvoltage from 4.said apparatus, va rst rectifier coupledto` said :circuitpa tuned circuit coupled to receive Signat-voltage from said apparatus, asecond rectier coupled to said tuned circuitfbias meansrconnectedfto prevent operation ofsaid nrst vrectifier untilfsaid signal voltage overcomes the bias, meansyfor .deriving a voltage from the iirst.:rectifler-.1and applying it asfarbiasfto Aanelem'ent-of-i said.fsec ond frectier to prevent substantial :increase `oi said toperatng voltage by 'said second `rectiiier with increase of lsaid signal voltage 'after the bias preventing. thecperation of said iirstv rectifier .is overcome, a low frequency amplifier, means coupling said second rectifier to theinput offsaid low frequency .amplien-and means `coupling the Aoutput ofsaid low frequency amplifier to said stopping means.

4. In signal tuned radio apparatus, 'variable `tuning means, means for Avarying saidttunlng means,means forstopping the variationoi said tuningmeans in response to an operating-voltage tuned by said tuning means, a tuned primary circuit coupled to receive signal voltage from said apparatus, avtriode rectifier tightly `coupled to said tuned primary'circuit a 'tunedvsecondary circuit coupled to 'said 4tuned primary circuit,V a second'rectiiier coupled to said tuned secondary circuit, bias means connected to prevent operation of said triode rectieruntil lsaidsignal'voltage overcomes the bias, means connecting the trioderectier to thesecond rectiiier toprevent substantial effective increase of said operating voltage with increase of said signal voltage after the bias is overcome and said triode rectifier operates, and means `coupling said secondrectier to said 'stoppingmeans 5. In 'signal tuned radio apparatus, vvariable tuning means, means for varying said tuning means,\a high frequency 4transformer having a tunedprimary and a tuned secondary winding,xa `triode rectier having a grid, 'coupling.s.means supplying a high frequency signalfrom saidprimary winding to the grid of said ltriode rectier, a second rectiiieig coupling 'means supplying `a high frequency signal "from said secondary .winding to said second rectifier, a resistorin "thecircuit of said triode rectifier, a resistor in the. circuit of said second rectifier, an electron .tubehavmg a grid and platecircuit, means coupling the negativeside orsaid second `rectiier 'resistor to the grid of said electrontube, means for terminating variation of. said tuningmeans in response to .a signal tuned bysaid tuning means coupled to the plate circuit of said .electronftubaand means connecting the positiveend Jof said V.triode rectifier. resistor to 'said 'second rectiiierito reduce the4 effective voltage of said second rectiiierfapplied to the grid of said electron tube.

v,6. In signal .tuned radio apparatus, `variable tuning means, means for varying .said tuning means, means for stopping the variationofsaid tuning means in response to ran operating voltage tuned by said tuning means, a circuit coupled to receive signal voltage from saidxapparatus, a i'irst .rectifier coupled to said circuit, a tuned circuit coupled to receive signal. voltage from said apparatus, `a contact `rectifier connected to said tuned vsecondary circuit,v means .coupling said contact rectier 'to 'said :stopping means, .bias means connected to preventvoperation of said first rectifier until said signal voltage overcomes the bias, and means' connecting said first rectifier to said contact rectifier whereby the additional operating voltage developed by said contact rectifier is neutralized by the voltage output of said first rectifier after the bias preventing the operation of the first rectifier is overcome.

7. In signal tuned radio apparatus, variable tuning'means, means for varying `said tuning means, a high frequency amplifier coupled to said variable tuning means, rectifing means connected to said high frequency amplifier, including a first resistor across which a rectified voltage develops, a second resistor connected to the high voltage end of' said first resistor, an electron tube having a grid and plate, a slider on said second resistor coupled to said grid, reproducing means coupled to said plate, relay means coupled to said plate, contact means operated by said relay to connect and disconnect the low voltage end of the second resistor to the corresponding end of the first resistor, whereby the position of said slider controls the strength of the signal applied to said reproducer when said contact is closed but does not control the strength of said signal to said relay means when said contact is open during tuning.

8. In signal tuned' radio apparatus, variable tuning means, means for varying said tuning means,` means for stopping the variation of said tuning means in response to an operating voltage tuned by said tuning means, a circuit coupled to receive signal voltage from said apparatus, a first rectifier coupled to said circuit, a tuned circuit coupled to receive signal voltage from said apparatus, a second rectifier coupled to said tuned circuit and adapted to supply an operating voltage, bias means connected to prevent operation of said first rectifier until said signal voltage overcomes the bias, means connecting said first rectifier to said second rectifier whereby the additional operating voltage developed by said second rectifier is neutralized by the voltage output of said first rectifier after the bias preventing the operation of the first rectifier is overcome, a low frequency amplifier, means coupling said second rectifier to the input of said low frequency amplifier, and means coupling the output of said low frequency amplifier to said stopping means.

9. In signal tuned radio apparatus, variable tuning means, means for varying said tuning means, means for stopping the variation of said tunning means in response to an operating voltage tuned by said tuning means, a circuit coupled to receive signal voltage from said apparatus, a first rectifier coupled to said circuit, a tuned circuit coupled to receive signal voltage from said apparatus, a second rectifier coupled to said tuned circuit, means to prevent rectification of said first rectifier in response to signal voltage below a predetermined value, means connecting the first rectifier to the second rectifier whereby the operating voltage developed by the second rectifier is reduced by the voltage output of the first rectifier, an audio amplier, means associated with the input of said audio amplifier including means coupling said input to said second rectifier adapted to respond only to a voltage having the polarity of said second rectifier, and means coupling the output of said audio amplifier to said stopping means.

10. In signal tuned radio apparatus, variable tuning means, means for varying said tuning means, means for stopping the variation of said tuning means in response to an operating voltage tuned by said tuning means, a circuit coupled to receive signal voltage from said apparatus, a first rectifier coupled to said circuit, a tuned circuit coupled to receive signal voltage from said apparatus, a contact rectifier coupled to said tuned circuit, means interconnecting said two rectifiers whereby the effective output of the contact rectifier is reduced by the operation of the first rectifier, and means coupling the output of said contact rectifier to said stopping means.

11. In signal tuned radio apparatus, variable tuning means, means for varying said tuning means, means for stopping the variation of said tuning means in response to an operating voltage tuned by said tuning means, a tuned' primary circuit coupled to receive signal voltage from said apparatus, a secondary circuit including a coil coupled to said primary circuit, a first rectifier connected to said secondary circuit, a tuned secondary circuit coupled to said tuned primary circuit, a second rectifier coupled to said tuned secondary circuit and adapted to function for tuning and for detection, means interconnecting said two rectifiers whereby the effective output of the second' rectifier is reduced by the operation of the first rectifier, means coupling said second rectifier to said stopping means, an audio amplifier, and means coupling said second rectifier functioning as a detector to said audio amplifier.

12. In signal tuned radio apparatus, variable tuning means, means for varying said tuning means, means for stopping the variation of said tuning means in response to an operating voltage tuned by said tuning means, a tuned primary circuit coupled to receive signal voltage from said apparatus, a secondary circuit including a coil coupled to said primary circuit, a first rectifier connected to said.' secondary circuit, a tuned secondary circuit coupled to said tuned primary circuit, a second rectifier coupled to said tuned secondary circuit, means interconnecting said two rectifiers whereby the effective output of the second rectifier is reduced by the operation of the first rectifier, means to prevent rectification of said first rectifier in response to signal voltage below a predetermined value, and means coupling said second rectifier to said stopping means.

13. In signal tuned radio apparatus, variable tuning means, means for varying said tuning means, a circuit coupled to receive signal voltage from said apparatus, a first rectifier coupled to said circuit, a tuned circuit coupled to receive signal voltage from said apparatus, a second rectifier coupled to said tuned circuit, means interconnecting said two rectifiers whereby the effective output of the second rectifier is reduced by the operation of the first rectifier, an electron tube having a plate and a grid, means connecting said grid to said second rectifier, and relay means connected to said plate for stopping the variation of said tuning means.

14. In radio apparatus, means supplying a signal of variable frequency, a utilization device, means to effect operation of said utilization device in response to a certain narrow frequency band of said variable frequency signal, including a circuit coupled to receive signal voltage from said apparatus, a first rectifier coupled to said circuit, a tuned circuit coupled to receive signal voltage from said apparatus, a second rectifier coupled to said tuned circuit, means to prevent rectiiication of said first rectifier in response to signal voltage below a predetermined value, means interconnecting said two rectiiers whereby theeiective output of the second rectifier is reduced by the operation of the rst rectier, and means coupling said second rectier to said utilization device.

l5.` In a signal tuned radio apparatus, variable tuning means, means for varying said tuning means, means for stopping the variation `of said tuning means .in response to an operating voltage tuned by said tuning means,v a tuned primary circuit coupled to receive signal voltage from said apparatus, a first rectier coupled to said tuned primary circuit, a tuned secondary circuit coupled to said tuned primary circuit, a second rectifier coupled to said tuned secondary circuit, bias means connected to prevent operation of said first rectifier until said signal Voltage overcomes the bias, means connecting the first rectifier to the second rectierI to prevent substantial efEective increase of said operating voltage Withincrease of said signal voltage after the bias on said first rectiiier isovercome, and means coupling said second rectifier to saidy stopping means.

1,6. In signal tuned radio apparatus, variable tuning means, means forl varying said tuning means, means for stopping the variation of said tuningmeansin responseto an operating voltage tuned by said tuning means', a circuitcoupled to Vreceive signal. voltage from said apparatus, a trode rectier ,having -a grid, plate and icathodecoupled `to said circuit, a `tunedcircuitcoupled:to receive signalvoltage from said apparatus, asecond rectifier` coupled to said tuned circuit, .meansto prevent rectification of said frstrectier in response to signalvoltage belowa predetermined value including bias meansconnected between said cathodel and grid -Wherebyxsaid grid ismade negativeV with respect to said cathode by-,a predetermined amount, means z-interconnectinggsaid two` rectiii'ers` whereby the. effective,:output` of the second rectifier is nreduced by the-operational?. the triode rectifier, and means' couplin'g'said second rectifier to said stopping means;

OLGIERD GIERWIATOWSKI.

REFERENCES" CITED 'The following references :are-l of record'in the -le of-.thisl patent:

UNITED STATES PATENTS Number vName Date 2,207,467 Mui-ler, July 9, -1940 2,262,218 Andrews Nov.- 11, 1941 

